Problem: Determine how many solutions exist for the system of equations. ${-6x+y = 10}$ ${6x-y = -10}$
Answer: Convert both equations to slope-intercept form: ${-6x+y = 10}$ $-6x{+6x} + y = 10{+6x}$ $y = 10+6x$ ${y = 6x+10}$ ${6x-y = -10}$ $6x{-6x} - y = -10{-6x}$ $-y = -10-6x$ $y = 10+6x$ ${y = 6x+10}$ Just by looking at both equations in slope-intercept form, what can you determine? ${y = 6x+10}$ ${y = 6x+10}$ Both equations have the same slope and the same y-intercept, which means the lines would completely overlap. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ Since any solution of ${-6x+y = 10}$ is also a solution of ${6x-y = -10}$, there are infinitely many solutions.